There exists in the prior art numerous systems for threading a shaft or holes in a workpiece. These systems may roughly be divided into three groups: a power group where the threading torque is applied under machine power; a T-handle group where the threading torque is applied manually on opposite sides of the threader (tap or die) such as with a T-shaped handle or bar; and a wrench group where the threading torque is applied manually on a single side of the threader such as with a Crescent.TM. wrench.
The power group requires the most costly tools of these three groups since there is needed a powered drill press that not only applies a downward force but also a rotational force to the threading tap or die. The disadvantages of this group become immediately apparent when attempting to thread hard material because when doing so, threading taps or dies are very easily broken or their threads are damaged. They break because to thread material properly, the constant application of threading torque is inappropriate. Instead, the threading torque should only be applied periodically, alternating with a reverse torque to clear any filings out of the threads. When periodically applying power torque, such constant reversal of the threading torque is time consuming and significantly increases the wear and tear on the drill chuck or holder. Furthermore, by being powered, a machinist is without any "feel" as to how much torque should be applied before reversing it. Additionally, when threading blind holes (holes which do not extend through a workpiece but instead have a bottom to them), this lack of "feel" often causes an operator to bottom out the threading tap against the bottom of the hole, which either will strip any threads previously grooved or will break the tap because the tap is still rotating but no longer moving axially. This type of failure is also applicable to power threading with a die when threading a stud extending from a workpiece. If the die should be rotated to thread the entire length of the stud and bottom out against the workpiece while still being rotated, the die or die teeth will either break or the threads previously grooved will be stripped. This, again, is due to an operator's lack of "feel" during the power threading process.
The T-handle group provides the "feel" lacking in the powered group, but one of its major disadvantages is its inability to be utilized under tight or close working conditions, such as in a corner. The outward extension of the T-handle requires considerable clearance around the area to be threaded. If a shorter T-bar is used to reduce the clearance required, then the machinist must apply more force to rotate the tap or die which becomes very tiring and inefficient should a large number of holes or shafts need to be threaded. Further, since the torque is manually applied, it is very easy for this torque to be applied at a skew angle and not aligned with the hole or shaft to be threaded. Additionally, the machinist must apply both a reversible rotational torque and a periodic downward force to the threader which increases the risk of grooving threads at a skew angle. Furthermore, both hands are necessary to rotate the T-handle group of threaders, thus preventing the machinist from guiding or providing some other needed operation simultaneous with the rotation of the threader.
The Crescent.TM. wrench group enables the threading of a hole or shaft in tight or closely confined quarters unlike the T-handle group but since the torque applied in the crescent wrench group is from one side only, there is a great probability that the hole or shaft threaded will be at a skew angle and not properly aligned as desired. Also, the wrench which is used is oftentimes unable to firmly and securely grip small threading taps without rounding the corners of the tap or otherwise being unable to grip a small area and rotate these taps. Further, by applying rotational force to only one side of the threader, a longer lever arm is required to generate the same torque with the same amount of applied force as is obtained by the T-handle group. This increases the chance of threading at a skew angle, and this longer arm reduces the ability of an operator to "feel" the threading of the hole or shaft. The longer lever arm and the lack of "feel" associated with this group increases the risk of "push-over," which is the application of too much sideways force and not enough downward force to the tap, which results in skew holes being drilled. Sufficient "feel" is necessary if the threader is to remain unbroken because otherwise too much rotational force may be applied without properly clearing filings from threads, thereby causing the tap or die to break. Furthermore, even with the single handle associated with this group, the operator's free hand is required for the application of a reverse torque and for stabilizing the threader in addition to properly aligning the threader with respect to the hole or shaft being threaded.
It is an object of this invention to enable the continuous alignment of the threading tap or die with an aligned workpiece and to do so such that the risk of threading at a skew angle is essentially eliminated. Another object is to enable one-handed application of the torque in addition to one-handed reversal of the applied torque, thus leaving the other hand available for other operations. A further feature is to enable holes or shafts to be threaded in tight or close quarters without the need for wide clearances on all its sides. Additionally, since an operator need only be directly concerned with the application of the rotational force, a "feel" for the material and its threading is enhanced.